Thyroid hormones have widespread effect on the rate of metabolism and oxygen consumption. They have notably profound effects on the heart, both on the strength and rate of the contractions. Marked changes in cardiac function occur in patients with hyper- or hypothyroidism. Cardiac contractility is increased in the hyperthyroid state and decreased in hypothyroidism and changes in specific proteins accompany these alterations.
The effect of thyroid hormone is mediated through binding of the hormone to thyroid hormone receptors which are nuclear proteins. The ligand-receptor complex binds to specific DNA motifs so called thyroid responsive elements (TRE) located in the promoter region of 3,5,3'-triiodothyronine (T-3) regulated genes. Through interaction with the transcriptional machinery of the cell, composed of ubiquitous and cell specific factors, the expression of the gene is positively or negatively regulated. Examples of genes of importance for cardiac funtion which are regulated by T-3 are the myosin heavy chains, .beta. adrenergic receptors and Na+K+ATPase.
Amiodarone, which for long has been used in therapy against many types of arrhythmias, acts as a competitive antagonist to thyroid action as defined by its dose dependent ability to .sup.1) compete with T-3 binding to the thyroid hormone receptor and .sup.2) inhibit T-3 induced increase in rat growth hormone (rGH) mRNA levels in cultured rat pituitary cells (Latham et al., J. Am. Coll. Cardiol Vol 9 (1987) pp 872-6; Norman and Lavin, J. Clin. Invest Vol 83 (1989) pp.)
The chemical structures of the T-3 receptor ligands disclosed herein are similar to that of amiodarone. Further, said ligands are T-3 antagonists. Thus, they are useful in the treatment of disorders which depend on the expression of T-3 regulated genes, such as heart arrhythmia and hyperthyroidism.